Apparatus for removing contaminants from high-resistivity fluids



Feb. 13, 1968 H. J. HALL 3,368,963

APPARATUS FOR REMOVING CONTAMINANTS FROM HIGH-RESISTIVITY FLUIDS Filed0013. 6, 1964 FIG. 1

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3o- I I 32 E: 5 58 a 3i i I! RESERVOIR 36 p p INVENTOR HERBERT J. HALLATTORNEYS United States Patent Ofifice 3,368,963 Patented Feb. 13, 19683,368,963 APPARATUS FOR REMOVING CGNTAMINANTS FROM HlGH-RESISTIVITYFLUEDS Herbert J. Hall, Skillman, N.J., assignor to Research- Cottrell,Inc., Bridgewater Township, N.J., a corporation of New JerseyContinuation-impart of application er. No. 369,689, May 25, 1964. Thisapplication Oct. 6, 1964, Ser. No. 405,004

4 Claims. (Cl. 204-302) ABSTRACT F THE DHSCLOSURE Single orseries-arranged units for removing and collecting particulate and liquidcontaminants from high resistivity fluids such as oils, fuels orsolvents utilize high voltage divergent electrostatic fields whichefiect a plurality of closely spaced electrostatic discharges into acontinuous fluid flow. The contaminants acquire a charge and areimpelled from the fluid and embedded in a replaceable porousnon-conducting matrix located adjacent the flow path, where they areheld by entrapment in the pores and by pressure of the electrostaticfield. The highly divergent field produced by a plurality of pointeddischarge electrodes provides turbulent mixing of the fluid, and thesynergistic combination of fluid turbulence and electrical field forceseifects optimum contaminant removal.

This application is a continuation-in-part of abandoned application Ser.No. 369,689 filed May 25, 1964.

This invention relates to a method and apparatus for the removal ofparticulate and liquid contaminants from generally non-conductive orhigh-resistivity fluids by means of electrostatic fields.

It is frequently desirable and important to remove liquid andparticulate contaminants from high-resistivity fluids and liquids,particularly insulating fluids such as petroleum based oils and thelike. This has been found to be quite difficult from a practicalstandpoint with filters of the kind wherein the fluid to bedecontaminated passes through the filter media, and it is characteristicof such filters that they shortly become clogged with solid materials,thus rendering the filter elements useless or at least of substantiallyreduced efficiency. At the same time, it is highly desirable to removecontaminating matter from such liquids in a continuous operation, thatis, while the liquid flows continuously through the apparatus used forseparating the contaminants from the liquid.

An important object of the present invention is to provide a novelelectrostatic method for driving contaminants which may be organic,inorganic, conductive, non-conductive, solid or immiscible liquids ormixtures thereof from a high-resistivity fluid to be cleaned rapidly andthoroughly into a matrix where they are held by entrapment in pores andby the pressure of the electrostatic field.

Another object is to provide such a device which will remove finelyentrained solids and/or water from dielectric liquids having highelectrical resistivity and high breakdown voltage. Eflective solidsdecontamination has been demonstrated with resistivities from to 10ohmcm and above, and breakdown voltage in excess of 40 volts/mil.

A further object is to provide such a device which will effectivelyremove contaminants from dielectric liquids having viscosities in therange of 0.5 to 600 centistokes.

A further object is to provide high voltage electric fields toaccomplish the results stated while the oil or other high-resistivityliquid flows through the fields.

A further object is to provide such a method wherein high voltageelectrodes impress very high electrostatic fields upon contaminants inthe liquid to be cleaned and the particulate or liquid contaminantsacquire electric charges and are driven into a porous non-conductingcollecting medium.

A further object is to provide an apparatus for carrying out the methodwherein pointed discharge electrodes project into the liquid to becleaned which flows between the electrodes and a porous matrix mediumadapted to hold contaminants which are embedded therein by the drivingforce of the electric field.

A further object is to provide an apparatus which provides a flow pathfor the dirty liquid having interposed in the flow path a conductingplate provided with pointed discharge electrodes projecting in spacedrelation toward a porous medium.

A further object is to provide a low pressure drop collector which willremove fine particles in the range of from 0 to about microns and such adevice that is particularly effective on fines below 5 microns.

A further object is to provide an apparatus of this character wherein aplurality of the electrostatic particle-removing units are seriallyarranged to subject the liquid to be cleaned to successive electrostaticaction of the type referred to as the fluid passes through thesuccessive units.

A further object is to provide simple and relatively light-weighthigh-resistivity fluid decontaminating apparatus particularly suited forboth stationary and mobile installations. For example, the improvedapparatus may comprise a portion of a packaging line for lubricating oilwith the oil passing through the decontaminator prior to being sealed incontainers. The assembly may also be mounted on an oil dispensingvehicle at air fields or the novel decontaminating apparatus may bemounted on its Own wheeled frame and form a portion of a mobile fluiddispensing system.

Other objects and advantages of the invention will become apparentduring the course of the following description.

In the drawing there are shown several embodiments of the inventionwherein:

FIGURE 1 is a sectional view illustrating the basic system with oneelectrostatic unit therein;

FIGURE 2 is a diagrammatic view showing a modified form of a continuoussystem, an electrostatic unit casing being shown in elevation with partsbroken away in section;

FIGURE 3 is a face view of an electrostatic plate showing one type ofelectrodes projecting therefrom;

FIGURE 4 is an edge elevation of the same;

FIGURE 5 is a face view of a modified type of plate; and

FIGURE 6 is an edge view of the same.

Throughout the specification and claims the term particulatecontaminants includes inorganic, organic, conductive, and non-conductivesolid particles and liquids immiscible in the high-resistivity fluid tobe cleaned by the method and in the apparatus of the present invention.

The terms non-conductive, high-resistivity or dielectric liquids meanliquids having resistivities in the order of about 10 to about 10ohm-cm. and above and liquids having breakdown voltages which may be inexcess of 40 volts/mil. These properties include almost all hydraulicfluids, lubricating oils, petroleum and synthetic base feed stocks, jetand turbine fuels, as well as many types of solvents used in cleaningoperations.

The effective removal of water can be achieved in the lower viscosityhigh-resistivity fluids, i.e., below about 50 centistokes down to thesolubility limits of water in the liquid to be cleaned. For petroleumbased liquids,

this is usually in the range of about 70 ppm. by weight at ambienttemperatures. However, water contamination levels as high as 1000 ppm.can be decontaminated in the apparatus of the invention. Levels of watercontamination higher than 1000 ppm. first should be precleaned with, forexample, mechanical water coalescers to levels of about 1000 ppm.

Referring to FIGURE 1, the numeral designates a casing, illustrated ascylindrical in transverse section and formed of any suitable material.The casing is provided with upper and lower heads 11 and 12 and throughthe non-conductive upper head 11 projects an electrical conductor 13which may be connected to the negative side of a high voltage powersupply. The conductor 13 is connected to an electrostatic dischargeplate 14 having spaced points 15 for the discharging of high voltageelectric charges therebeneath. Spaced below the plate 14 and supportedon the bottom conductive plate 12 is arranged one or more matrices 16which may be formed of any suitable porous material, for example,polyurethane foam. The lower matrix, as illustrated, may be supporteddirectly on the bottom plate 12, and the latter is grounded as at 17 orconnected to the other pole of the high voltage power supply.

Connected to the casing 10 is an inlet duct 18 through which is feddirty high-resistivity liquid, that is, an oil or the like generallynon-conductive liquid containing particulate matter and/or contaminatingconductive immiscible liquids such as water to be removed in theapparatus. The cleaned and decontaminated liquid flows from theapparatus through an outlet duct 19. The ducts 18 and 19 and the space20 beneath the discharge electrode 14 constitute a flow path for theoil, and under the influence of the high voltage electric charges fromthe points of electrodes 15, the contaminating matter is drivendownwardly into the matrix 16, as further described below.

The particulate particles are primarily driven into the non-conductingmatrix by virtue of the turbulent mixing of the fluid due to the highlydivergent field and are held in the non-conducting matrix by the chargeinduced on the particulate matter. Thus, two principal forces arecooperating in the particulate removal process: turbulent fiow of liquidand electric field forces, both projecting the particles through theliquid into the matrix. The synergistic effects of high electric fieldstrength and turbulence in cooperation with the matrix medium providethe efiicient cleaning of the system.

A modified form of a somewhat more sophisticated system is shown inFIGURE 2 in which an axially elongated casing 24 is provided having aconducting rod 25 extending axially through the greater portion of thelength thereof. This rod may be suitably supported at its upper end byan electrical insulator 26 and connected to a high voltage cable 27leading to a source of power supply 28. A second terminal of the powersupply is connected to a cable 30 grounded as at 31, and the cable 30 isconnected as at 32 to the casing 24, which will be of conductingmaterial for a reason which will become apparent.

Adjacent the bottom thereof the casing 24 is provided with a conductivesupporting plate 34 on which rests a matrix 35 of the type referred toabove. The space 36 beneath the bottom plate is part of a circulatorysystem to be described.

In a plane spaced above the matrix 35 is arranged another matrix 38fixed in any suitable way to a conducting plate 39 over which issupported another matrix 40. In the space between the matrices 35 and 38is arranged an electrostatic plate 41 secured about central opening 49to the conducting rod 25. The plate 41 is provided with downwardlyprojecting needle-like electrodes 42 and upwardly projecting needle-likeelectrodes 43, and both sets of these electrodes may be of the same typeas the electrodes 15 in FIGURE 1. The plate 41 and associated 4electrodes are shown in FIGURES 3 and 4. It will be noted in FIGURE 3that the electrodes are substantially equidistantly spaced from eachother radially and circumferentially to provide uniform distribution ofindividual highly divergent electric field sources opposite thecooperating matrix.

The plate 34 and matrix 35 are each provided with an axial opening 46therethrough of substantially larger diameter than the conducting rod 25for the flow of liquid from the space or chamber 36 into the space 47around the plate 41. The matrix unit comprising the matrices 38 and 40and plate 39 is similarly apertured as at 49. Above the matrix 40 isanother of the chambers 47 surrounding a further electrostatic plate 41and associated electrodes secured to rod 25, and it will be apparentthat the unit comprising elements 38, 39 and 40 is similarly repeated atintervals substantially throughout the height of the casing 24, and theplates 39 and 34 of the various matrix units are grounded on the casing24 and are thus connected to the power supply through conductors 32 and30.

The high-resistivity liquid to be treated flows into the chamber 36through an inlet pipe 52 in which are arranged a valve 53 and pump 54.Liquid from the top of the casing 24 is discharged through a pipe 55having a valve 56 therein. From the pipe 55, a pipe 58, valved as at 59,leads to a reservoir 60 and from the reservoir a pipe 61, valved as at62, leads to the inlet pipe between the valve 53 and pump 54. Variousmodifications of the system may be resorted to, for example, for thepurpose of recirculating the liquid from the pipe 55 to the pipe 54,such alternative means forming per se no part of the present invention.

Various types of electrostatic discharge plates may be employed assuggested in FIGURES 5 and 6. In these figures, a circular p ate 65, ofsuitable sheet metal, and similar in size and purpose to the plate 41,may be struck to provide pointed fingers 66 to provide the electrostaticdischarge electrodes.

OPERATION It will become apparent that although negative polarity highvoltage DC energization is shown for use with the system, otherarrangements may be used such as positive polarity, AC and pulseenergization as is known in the electrostatic precipitaion art. In theform of the invention shown in FIGURE 1, the liquid to be cleaned is fedcontinuously through the duct 18, through space 20 and outwardly throughduct 19. The high voltage electrodes 15 impress a very high electricfield in the vicinity of the points of the electrodes and the particlessuch as fine road dust, metallic fines, water and the like in the oilbeing cleaned acquire an electric charge, negative in the present case.These particles are driven into the porous matrix medium under theinfluence of the electric field. The electrical discharge also createsturbulence in the liquid being decontaminated which assists in bringingthe particulate material into an effective zone of one or more of theelectric discharge fields, thus improving the efiiciency of theapparatus. The porous matrix holds particles which have been embeddeddeeply therein by the pressure and force of the electric field. Oilheavily contaminated with aluminum powder, for example, can be clarifiedusually in a few minutes. Electric fields corresponding to 20 to 60k.v./ inch are typical but not restrictive.

In the form of the invention shown in FIGURE 2, the liquid is subjectedto repeated electrostatic discharge actions. With the valves 59 and 62closed and the valves 53 and 56 open, liquid will be pumped into thechamber 36, upwardly through the opening 46 and will pass into thechamber 47 to flow radially outwardly of the plate 41, thence radiallyinwardly and into the next upper chamber 47 through the opening 49. Thusthe liquid is subjected to repeated electrostatic action in thesuccessive chambers 47 and the liquid is discharged through the pipe 55and suitably collected. If desired, the valve 56 may be closed and thevalve 59 opened, in which case the liquid will flow into the reservoir60. If it should be desired to re-treat the liquid in the reservoir, thevalve 62 may be opened, in which case liquid from the reservoir will bepumped through the casing 24 in the manner described. If recirculationis to be resorted to, the valves 53 and 56 may be closed, after thesystem is charged with the liquid to be cleaned, and the valves 59 and62 opened, in which case the liquid will be recirculated through thereservoir as many times as desired and then discharged by closing thevalve 59 and opening the valve 56.

The method and apparatus affords substantial advantages in use.Super-cleaning of some fluids is not only feasible but can be done on aunipass basis in a continuous industrial production system. Highperformance can be obtained with relatively small-size equipmentrequiring a very low pressure drop between the inlet and outlet and withnegligible electrical power consumption. Unipass removal efliciency ofat least 99 percent can be readily achieved on micron particles (finesbelow 5 micron are similarly removed as indicated by silting indices).Effective removal of particles typically occurs in the 0 to 100 micronrange. Moreover, the apparatus is operative with substantial differencesin temperatures and pressures.

The particular material employed in the matrices is optional, so long assuch material is porous and not soluble in the fluids being treated; forexample, tests have been made using a cotton gauze-like pad. Under theimpact of the particles pores of the pad are opened and expanded, thusallowing additional dirt to be deposited within the medium. It has beenfound that whenever suitable matrix material has been used, entrapmentto a substantial extent takes place, a greater quantity of particlesbeing entrapped than can be accommodated through any filters throughwhich the liquid passes. In addition to cotton pads, typical matrixmedia may comprise plastic foams made from polyurethane, Teflon and thelike, glass fibers, sintered ceramics, etc.

The use of very sharp electrode points provides highly localizedelectric fields, and subjects the particles to high pressure whichdrives them into the matrix where they are retained. It has also beenfound that loose or resilient matrix media will expand as it becomesfilled with particles, thus allowing more particles to be driven in tosecure maximum use of the matrix collectors. The pore sizes of thematrix do not have to be made small to accept and hold fine particles,since the electric field drives the particles deep within the matrix. Avery satisfactory matrix has been made from polyurethane foam having 60pores per linear inch and a thickness in the order of about inch. Unlikea filter, no pressure drop occurs through the presence of the matrixsince the latter is not arranged in the line of flow. Tests usingmatrices having 30 to 80 pores per linear inch have provided verysatisfactory decontamination of high-resistivity liquids.

From the foregoing it will be apparent that the apparatus is highlyeffective in carrying out its intended function, as is true of thedirectly related method. As to the method, it involves projecting anelectrostatic field into a flowing body of liquid to drive particlestherefrom into a collecting matrix which entraps the particulatematerial without restricting the flow of the liquid. The method alsoinvolves the use of a substantial number of electrostatic discharges soas to effectively subject the flowing liquid to a number of fields forthe effective driving of particles from the liquid, and the use of theforce imparted to the particles to embed the particles in aparticle-collecting matrix. The method also contemplates utilizing thehigh voltage discharges for creating turbulence in the liquid as itpasses through the discharge fields to insure a more eflicient removalof the particulate material from generally non-conductive liquids orliquid mixtures.

It has been found that the method and apparatus are Example I An oilcommercially available under the trademark Sunvis 931 having a viscosityrange of 200 centistokes at 70-100 F. and an electrical resistivity of'1.0 10 ohm-cm. at applied voltages of less than about 5 k.v. DC/inchwas contaminated with water and about 1 gram of particulate material pergallon of oil or 300 ppm. by weight. The contaminated 'oil was passedthrough apparatus of the type illustrated in FIGURE 1 wherein the totalplate area was 60 sq. inches and the discharge plate was provided withdischarge points. The matrix consisted of A inch polyurethane foamporosity grade 45-80 p.p.i. The discharge point to foam surface wasabout A inch. Initially, the applied voltage was 8 k.v. However, as themoisture was removed from the oil the voltage was raised to 20 k.v. (40k.v./inch average field strength). The electrical breakdown of thecleaned oil increased to more than k.v. DC/inch indicating the removalof moisture as well as particles.

Example 11 A petroleum naphtha feedstock having a viscosity of 0.5-1.0at 70-90 F. was contaminated with Arizona road dust having the followingtypical particle size distribution by weight.

Percent:

12 5y. 24 10 44 30p. 100 200 t The contaminated feedstock was passedthrough the apparatus described in Example I except the polyurethanematrix was replaced by a cotton gauge matrix sewn to the plate electrodeand 99% of the contaminant was removed on a single pass.

Example III Kerosene purchased locally having the following as receivedanalysis:

was mixed with wax.

The wax used in the test was typical of that found in fuel oil.

The cloud points were determined by slowly cooling samples in anenvironmental chamber and noting the temperatures at which wax crystalsfirst formed.

A solution of about 1.8% wax by weight in kerosene was prepared fortreating in a 1.5 gallon electrostatic filter of the type illustrated inFIGURE 2. The cloud point of this solution was 6.8 F. With an ambienttemperature of 82 F. and between 15-20 k.v. on the filter, thekerosene-wax solution was recirculated for a filter residence time of 12minutes and a sample taken. The cloud point of this sample was 6.8 F. orno different than before electrostatic treatment.

The above solution was cooled to 6.8 F. while mixing in the reservoirand recirculating through the de-energized filter. At this temperature,wax crystals started to form and the solution was then held at atemperature between 5 and 6.8 F. and 20 k.v. applied to the filter.Samples were taken after 1.8, 4 and 12 minute filter residence times.The solution was essentially clear of crystals after 1.8 minutes. Allthree samples had the same cloud point of 3.2 F. or a drop of 3.6 F.Subsequent cooling down to -5.8 F. with additional wax crystallizationfollowed where fluid velocity equals fluid flow rate (g.p.m.) X 231effective filter cross-section (in?) It is to be understood that thesteps in the method and the details of construction of the apparatus areillustratively described and shown and that changes therein may be madewithout departing from the spirit of the invention or the scope of theappended claims.

I claim:

1. Apparatus for separating particulate contaminants from ahigh-resistivity liquid comprising an elongated casing, a plurality ofgrounded electrically conducting plates in said casing arrangedtransversely thereof and spaced from each other, an electricallyconducting electrostatic discharge plate in said casing arranged betweeneach adjacent pair of grounded plates, a porous matrix carried by eachgrounded plate at the side thereof facing the associated dischargeplate, said matrices and said grounded plates having openingstherethrough to form a liquid flow path through each grounded plate andits associated matrix, radially outwardly around the associateddischarge plate, radially inwardly of said grounded plate and throughthe next opening, means for effecting a fluid flow through said path,and means for subjecting each discharge plate to a high voltage current.

2. Apparatus according to claim 1 wherein each discharge plate isprovided with pointed electrodes dispersed over and projecting from atleast one side thereof to provide a plurality of electrostatic dischargepoints from each discharge plate.

3. Apparatus according to claim 1 wherein each discharge plate isprovided with pointed electrodes dispersed over and projecting from eachface thereof to subject the liquid to a plurality of electrostaticdischarge points from each side of each discharge plate.

4. Apparatus according to claim 1 wherein said means for subjecting saiddischarge plates to high voltage current comprises a conducting rod insaid casing of smaller diameter than and projecting through saidopenings in the grounded plates, said rod being electrically connectedto said discharge plates and supporting the latter in said casing.

References Cited UNITED STATES PATENTS 661,189 11/1900 Olsen et al.2l0266 1,414,079 4/1922 Giebner 204--305 2,116,509 5/1938 Cottrell204--302 3,190,827 6/1965 Kok et al. 204302 3,252,885 5/1966 Griswold204--302 HOWARD S. WILLIAMS, Primary Examiner.

JOHN H. MACK, Examiner.

T. TUFARIELLO, Assistant Examiner.

